Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence of the materials. This is often accomplished by melting the base material of a workpiece and a filler material together to form a molten pool (weld pool) that cools to become a strong joint, typically stronger than the base material. Welding differs from soldering and brazing, which involve melting a lower-melting point material between base materials to form a bond therebetween.
A common method of welding is arc welding. Arc welding uses a power supply to create an electric arc between an electrode (the filler material) and the workpieces, melting base and filler material at a welding point, weld joint or seam. The welding area is often protected from oxidation by some type of inert material, such as a gas, or a filler material.
In shielded metal arc welding, also known as manual metal arc welding or stick welding, an electric current is used to strike an arc between the workpiece and a consumable electrode rod. The electrode rod is made of steel and covered with a flux. The flux protects the weld area from oxidation and contamination by producing carbon dioxide gas during the welding process. The electrode rod core acts as a filler material, thus obviating the need for a separate filler material.
In submerged arc welding, commonly referred to as SAW, a continuously fed consumable electrode serves to create an electrical arc with the workpiece. The molten weld and the arc zone are protected from atmospheric contamination by being submerged under a fusible flux. When molten, the flux becomes conductive and produces a current path between the electrode and the workpiece. The layer of flux completely covers the molten metal thus preventing spatter and sparks as well as suppressing ultraviolet radiation and fumes associated with the welding process.
Submerged arc welding can be mechanized and automated. Mechanized and automated submerged arc welding processes are usually limited to flat horizontal welding positions. Automated submerged arc welding machines are generally supported on a self-propelled, welding carriage that is capable of guiding itself.
Self-guiding welding carriages currently being used are either guided along permanently placed tracks or rails, or guided by a crabbing arm aligned relative to a vertical flange or rail. Welding carriages that are guided along a permanently placed track is limited in portability of the welding carriage and is also limited to smaller fabrication projects. Projects involving welding large dimensioned objects typically require a larger dimensional welding carriage and often can include the use of a gantry or crane.
Another disadvantage of a welding carriage guided along a permanently placed track is the placement of the object to be welded. As the tracks are permanently placed, the workpiece must be precisely placed parallel to the track, for aligning the welding machine relative to the weld seam. A slight misalignment of the welding machine can result in a misplaced weld seam. Quite often, workpieces are of substantial weight thus requiring the aid of a crane. Precisely placing a heavy workpiece with a crane parallel to the track, to align the welding machine with the weld seam, is difficult and can take large amounts of time.
Self-guiding welding carriages also have the disadvantage of not being able to be self-aligning. The welding carriages are guided along a rigid track or rail. The self-guiding welding machines travel along a substantially straight line, and does not deviate from the track or rail. However, during the welding process, the workpiece and thus its base material, such as metal, is subjected to localized extreme heat. The localized heating of the base material can cause it to expand differentially and result in the warping or distortion of the base material. Even after the welding machine is precisely aligned parallel to the track or rail of the welding carriage, the warping caused by the heat usually causes the weld seam to shift. This necessitates stoppage of the welding process to re-align the welding machine, significantly increasing the time to complete a welding project.
Further, permanently placed tracks or rails usually require a large amount of real estate that is specifically designated for welding. Such equipment, including larger gantries, are not readily mobile. Welding machines and carriages must be brought to the tracks or rails and thus welding projects must be performed at specific locations only.